@section Time zones and mappings

All tools of the dateutils suite support @samp{--from-zone=ZONE} to
globally declare that date/time input is expressed in ZONE.

Tools that output absolute date/times also allow @samp{--zone=ZONE} to
globally declare that date/time output is to be converted into ZONE.

When input or output zones are omitted dates and timestamps are treated
as coming from the special (built-in) timezone UTC.

Due to the complexity in setting up and maintaining timezone reference
data, we decided to depart from our usual course and depend on the
system's zoneinfo database.  As a consequence, @samp{ZONE} can point to
anything in the system's zoneinfo directory which is assumed to be in
IANA format.

Zones @samp{UTC}, @samp{TAI}, and @samp{GPS} are treated specially.
Their rules and offsets are built-in and never read from the disk.

@heading Timezone maps

Additionally, and true to our motto not to depend on system facilities,
dateutils ships with timezone map files to map domain specific
identifiers to their IANA zoneinfo name.

Mapped timezone identifiers generally look like @samp{DOMAIN:IDENTIFIER}
where @samp{DOMAIN.tzmap} is a file in the tzmap search path and
@samp{IDENTIFIER} is a valid entry therein.  In-lieu of @samp{ZONE}
specifiers of the above form are accepted by all tools of the dateutils
suite as well.

For more information on timezone map files, covered domains and licence
information visit @url{http://www.fresse.org/dateutils/tzmaps.html}.
